I have tried different indices, and everything works fine for i<=17, but starting from 18 I can not access to p10[i] without an immediate freeze.
The bug does not depend on system: I tried macOS and Windows 10, both lead to the same result.

Note that counting the number of posets on a given set is very hard (and related to counting finite topologies), the human kind is not even able to count the posets on 17 elements (yet). If we could iterate on them in a fast way, we would also be able to count them easily. See https://oeis.org/A000112 for the first values (they are hardcoded in Sage with Posets(i).cardinality()).